U.S. patent application number 16/095588 was filed with the patent office on 2019-04-11 for non-humidified proton-conductive membrane, method for producing the same, and fuel cell.
This patent application is currently assigned to NATIONAL UNIVERSITY CORPORATION NAGOYA UNIVERSITY. The applicant listed for this patent is NATIONAL UNIVERSITY CORPORATION NAGOYA UNIVERSITY. Invention is credited to Takato KAJITA, Yushu MATSUSHITA, Takahiro MORI, Atsushi NORO.
Application Number | 20190109343 16/095588 |
Document ID | / |
Family ID | 60116074 |
Filed Date | 2019-04-11 |
United States Patent
Application |
20190109343 |
Kind Code |
A1 |
NORO; Atsushi ; et
al. |
April 11, 2019 |
NON-HUMIDIFIED PROTON-CONDUCTIVE MEMBRANE, METHOD FOR PRODUCING THE
SAME, AND FUEL CELL
Abstract
A non-humidified proton-conductive membrane according to the
present invention includes a polymer and a proton-conductive
substance. The polymer includes a glassy or crystalline first site
having a glass-transition temperature or melting temperature higher
than the service temperature of the proton-conductive membrane and
a second site capable of forming a noncovalent bond. The
proton-conductive substance includes a proton-releasing/binding
site capable of noncovalently binding to the second site of the
polymer and a proton coordination site capable of coordinating to
protons, the proton-releasing/binding site and the proton
coordination site being included in different molecules that
interact with each other or being included in the same molecule. A
proton-conductive mixed phase that includes the second site to
which the proton-releasing/binding site of the proton-conductive
substance is bound and the proton-conductive substance is lower
than the service temperature of the proton-conductive membrane. The
amount of the proton-releasing/binding site is excessively large
compared with the amount of the second site of the polymer.
Inventors: |
NORO; Atsushi; (Nagoya-city,
JP) ; KAJITA; Takato; (Nagoya-city, JP) ;
MORI; Takahiro; (Nagoya-city, JP) ; MATSUSHITA;
Yushu; (Nagoya-city, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL UNIVERSITY CORPORATION NAGOYA UNIVERSITY |
Nagoya-shi, Aichi |
|
JP |
|
|
Assignee: |
NATIONAL UNIVERSITY CORPORATION
NAGOYA UNIVERSITY
Nagoya-shi, Aichi
JP
|
Family ID: |
60116074 |
Appl. No.: |
16/095588 |
Filed: |
March 27, 2017 |
PCT Filed: |
March 27, 2017 |
PCT NO: |
PCT/JP2017/012358 |
371 Date: |
October 22, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/02 20130101; C08L
33/066 20130101; C08L 27/22 20130101; C08J 2327/18 20130101; H01M
8/10 20130101; Y02P 70/50 20151101; C08L 101/06 20130101; C08J
2355/00 20130101; C08F 293/005 20130101; C08J 5/18 20130101; H01M
8/1044 20130101; H01M 8/1048 20130101; H01M 2300/0091 20130101;
C08F 2438/03 20130101; C08J 5/2231 20130101; C08J 2327/22 20130101;
C08J 2333/14 20130101; C08L 101/12 20130101; C08K 5/42 20130101;
H01M 8/1041 20130101; C08J 2455/00 20130101; C08J 5/225 20130101;
C08F 212/08 20130101; H01M 2008/1095 20130101; C08F 2438/00
20130101; C08K 5/06 20130101; H01M 2300/0082 20130101; Y02P 70/56
20151101; H01M 8/1081 20130101; C08J 2453/00 20130101; C08J 5/22
20130101; H01B 1/04 20130101; C08J 5/2237 20130101; C08L 27/22
20130101; C08K 5/053 20130101; C08L 53/00 20130101; C08F 212/08
20130101; C08F 226/06 20130101 |
International
Class: |
H01M 8/1044 20060101
H01M008/1044; C08F 293/00 20060101 C08F293/00; C08L 27/22 20060101
C08L027/22; C08L 33/06 20060101 C08L033/06; C08J 5/22 20060101
C08J005/22; H01M 8/1048 20060101 H01M008/1048; H01M 8/1081 20060101
H01M008/1081 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2016 |
JP |
2016-085786 |
Claims
1. A non-humidified proton-conductive membrane that is a
proton-conductive membrane having proton conductivity under a
non-humidified condition, the proton-conductive membrane
comprising: a polymer including a glassy or crystalline first site
having a glass-transition temperature or melting temperature higher
than a service temperature of the proton-conductive membrane, and a
second site including a functional group capable of noncovalently
binding to another molecule; and a proton-conductive substance
including a proton-releasing/binding site capable of released
protons and a proton coordination site capable of coordinating to
the protons, the proton-releasing/binding site including a
functional group capable of noncovalently binding to the second
site of the polymer, the proton-releasing/binding site and the
proton coordination site being included in different molecules that
interact with each other or being included in the same molecule, a
proton-conductive mixed phase having a glass-transition temperature
lower than the service temperature of the proton-conductive
membrane, the proton-conductive mixed phase including the second
site to which the proton-releasing/binding site of the
proton-conductive substance is bound and the proton-conductive
substance, the amount of the proton-releasing/binding site being
excessively large compared with the amount of the second site of
the polymer.
2. The non-humidified proton-conductive membrane according to claim
1, wherein the functional group of the second site is a basic
group, and the functional group of the proton-releasing/binding
site is an acidic group.
3. The non-humidified proton-conductive membrane according to claim
2, wherein the basic group is a nitrogen-containing heterocycle,
and the acidic group includes at least one selected from a carboxyl
group, a phosphate group, a sulfo group, and a sulfonylimide
group.
4. The non-humidified proton-conductive membrane according to claim
3, wherein the acidic group includes at least one selected from a
sulfo group and a sulfonylimide group.
5. The non-humidified proton-conductive membrane according to any
one of claim 1 to 4, wherein the proton coordination site includes
at least one selected from an ether linkage, an ester group, an
alcohol group, a ketone group, and an amide group.
6. The non-humidified proton-conductive membrane according to any
one of claim 1 to 5, wherein the proton coordination site includes
at least one selected from an ether linkage and an alcohol
group.
7. The non-humidified proton-conductive membrane according to any
one of claim 1 to 6, wherein the proton-conductive substance is a
mixture of a substance X including the proton-releasing/binding
site with a nonaqueous substance Y including the proton
coordination site and interacting with the substance X, wherein the
substance X includes at least one selected from a polymer having a
side chain including a sulfo group and a fluorine compound
including a sulfonylimide group, and wherein the substance Y
includes at least one selected from a protic solvent including an
ether linkage and a polymer including an alcohol group.
8. The non-humidified proton-conductive membrane according to any
one of claim 1 to 6, wherein the proton-conductive substance is a
single pure substance including the proton-releasing/binding site
and the proton coordination site in the same molecule and is a
disulfonic acid including an ether linkage.
9. A method for producing the non-humidified proton-conductive
membrane according to any one of claim 1 to 8, the method
comprising: (a) dissolving or dispersing the polymer and the
proton-conductive substance in a solvent to form a mixed solution
or dispersion; and (b) evaporating the solvent included in the
mixed solution or dispersion to produce the non-humidified
proton-conductive membrane.
10. A fuel cell comprising an anode, a cathode, and the
non-humidified proton-conductive membrane according to any one of
claim 1 to 8, the proton-conductive membrane being interposed
between the anode and the cathode.
Description
TECHNICAL FIELD
[0001] The present invention relates to a non-humidified
proton-conductive membrane, a method for producing the
proton-conductive membrane, and a fuel cell.
BACKGROUND ART
[0002] A fuel cell is composed primarily of a solid electrolyte
membrane that conducts protons and a pair of electrodes including a
catalyst between which the solid electrolyte membrane is
interposed. Perfluorosulfonic acid membranes, such as Nafion
(registered trademark, the same applies hereinafter), have been
conventionally used as a solid electrolyte membrane. However, it is
necessary to humidify a perfluorosulfonic acid membrane for
increasing the proton conductivity of the perfluorosulfonic acid
membrane. Accordingly, a humidifying system needs to be used when
electric power is generated using such a fuel cell. Installation of
the humidifying system disadvantageously increases the size of the
entire fuel cell apparatus, the amount of time and effort required,
and the maintenance costs. Under these circumstances, power
generation in a non-humidified system has been studied. A
polybenzimidazole/phosphoric acid mixed system has been developed
as a non-humidified proton-conductive membrane (e.g., see PTL 1 and
NPL 1). In this system, imidazole units and phosphate ions serve as
temporal proton carriers.
CITATION LIST
Patent Literature
[0003] PTL 1: International Publication No. 1996/13872
Non Patent Literature
[0003] [0004] NPL 1: J. Electrochem. Soc., Vol. 142, No. 7, 1995,
pp. 121-123
SUMMARY OF INVENTION
Technical Problem
[0005] However, in the case where the polybenzimidazole/phosphoric
acid mixed system is used, molecules of phosphoric acid may elute
during power generation and, consequently, proton conductivity may
be reduced after a long period of use. Accordingly, the development
of a non-humidified proton-conductive membrane other than the
polybenzimidazole/phosphoric acid mixed system has been
anticipated.
[0006] The present invention was made to address the above issues.
A primary object of the present invention is to provide a novel
non-humidified proton-conductive membrane.
Solution to Problem
[0007] A non-humidified proton-conductive membrane according to the
present invention is a proton-conductive membrane having proton
conductivity under a non-humidified condition,
[0008] the proton-conductive membrane including:
[0009] a polymer including a glassy or crystalline first site
having a glass-transition temperature or melting temperature higher
than a service temperature of the proton-conductive membrane, and a
second site including a functional group capable of forming a
noncovalent bond; and
[0010] a proton-conductive substance including a
proton-releasing/binding site (i.e., a third site) capable of
releasing protons and a proton coordination site (i.e., a fourth
site) capable of coordinating to the protons, the
proton-releasing/binding site including a functional group capable
of noncovalently binding to the second site of the polymer, the
proton-releasing/binding site and the proton coordination site
being included in different molecules that interact with each other
or being included in the same molecule,
[0011] a proton-conductive mixed phase having a glass-transition
temperature lower than the service temperature of the
proton-conductive membrane, the proton-conductive mixed phase
including the second site to which the proton-releasing/binding
site of the proton-conductive substance is bound and the
proton-conductive substance,
[0012] the amount of the proton-releasing/binding site being
excessively large compared with the amount of the second site of
the polymer.
[0013] In the non-humidified proton-conductive membrane according
to the present invention, the glass-transition temperature or
melting temperature of the first site is higher than the service
temperature of the proton-conductive membrane, and the
glass-transition temperature of the proton-conductive mixed phase
that includes the second site to which the proton-releasing/binding
site of the proton-conductive substance is bound and the
proton-conductive substance is lower than the service temperature
of the proton-conductive membrane. Consequently, during the use of
the non-humidified proton-conductive membrane according to the
present invention, the first site is in a solid state, while the
proton-conductive mixed phase that includes the second site and the
proton-conductive substance is in a molten state (i.e., in rubber
form) and, as a whole, the proton-conductive membrane forms a
proton-conductive soft elastomer membrane that does not become
fluidized and retains its original shape. Furthermore, since the
amount of the proton-releasing/binding site is excessively large
compared with the amount of the second site of the polymer, free
protons are likely to be generated from the
proton-releasing/binding site. This greatly contributes to the
conduction of protons. Moreover, in the non-humidified
proton-conductive membrane according to the present invention, the
proton coordination site of the proton-conductive substance serves
as a temporal proton carrier and has high molecular mobility. This
enables the proton-conductive membrane to exhibit good proton
conductivity even under a non-humidified condition.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a schematic diagram illustrating a non-humidified
proton-conductive membrane.
[0015] FIG. 2 is a schematic diagram illustrating a non-humidified
proton-conductive membrane.
[0016] FIG. 3 is a cross-sectional view of a fuel cell 10.
[0017] FIG. 4 is a schematic diagram illustrating a
proton-conductive soft elastomer membrane prepared in Example
1.
[0018] FIG. 5 is a schematic diagram illustrating a
proton-conductive soft elastomer membrane prepared in Example
4.
[0019] FIG. 6 is a schematic diagram illustrating a
proton-conductive soft elastomer membrane prepared in Example
5.
DESCRIPTION OF EMBODIMENTS
[0020] A preferred embodiment of the present invention is described
below.
[0021] A non-humidified proton-conductive membrane according to the
embodiment includes a polymer and a proton-conductive substance as
illustrated in FIG. 1 or 2. The polymer includes a glassy or
crystalline first site having a glass-transition temperature or
melting temperature higher than the service temperature of the
proton-conductive membrane and a second site including a functional
group capable of forming a noncovalent bond. The proton-conductive
substance includes a proton-releasing/binding site (i.e., a third
site) capable of released protons and noncovalently binding to the
second site of the polymer and a proton coordination site (i.e., a
fourth site) capable of coordinating to the protons. The
proton-releasing/binding site and the proton coordination site are
included in different molecules that interact with each other or
are included in the same molecule. A proton-conductive mixed phase
that includes the second site to which the proton-releasing/binding
site of the proton-conductive substance is bound and the
proton-conductive substance has a glass-transition temperature
lower than the service temperature of the non-humidified
proton-conductive membrane. The amount of the
proton-releasing/binding site is excessively large compared with
the amount of the second site of the polymer.
[0022] Since the glass-transition temperature or melting
temperature of the first site of the polymer is higher than the
service temperature (e.g., 80.degree. C. or 95.degree. C.) of the
non-humidified proton-conductive membrane, the first site is glassy
or crystalline at the service temperature of the non-humidified
proton-conductive membrane. Examples of the first site include, but
are not limited to, oligostyrenes, oligoacrylic acid esters,
oligomethacrylic acid esters, oligo-olefins, oligosulfones,
oligoarylates, oligoether ketones, oligoetherimides, oligophenylene
sulfides, oligophenylene ethers, oligocarbonates,
oligobenzimidazoles, and oligofluoroethylenes. Examples of the
oligostyrenes include oligostyrene, oligoacetylstyrene,
oligoanisoylstyrene, oligobenzoylstyrene, oligobiphenylstyrene,
oligobromoethoxystyrene, oligobromomethoxystyrene,
oligobromostyrene, oligobutoxymethylstyrene,
oligo-tert-butylstyrene, oligobutyrylstyrene,
oligochlorofluorostyrene, oligochloromethylstyrene,
oligochlorostyrene, oligocyanostyrene, oligodichlorostyrene,
oligodifluorostyrene, oligodimethylstyrene,
oligoethoxymethyistyrene, oligoethoxystyrene,
oligofluoromethylstyrene, oligofluorostyrene, oligoiodostyrene,
oligomethoxycarbonylstyrene, oligomethoxymethylstyrene,
oligomethylstyrene, oligomethoxystyrene, oligoperfluorostyrene,
oligophenoxystyrene, oligophenylacetylstyrene, oligophenylstyrene,
oligopropoxystyrene, oligotoluoylstyrene, and
oligotrimethylstyrene. Examples of the oligoacrylic acid esters
include oligoadamantyl acrylate, oligo-tert-butyl acrylate,
oligo-tert-butylphenyl acrylate, oligocyanoheptyl acrylate,
oligocyanohexyl acrylate, oligocyanomethyl acrylate,
oligocyanophenyl acrylate, oligofluoromethyl acrylate,
oligomethoxycarbonylphenyl acrylate, oligomethoxyphenyl acrylate,
oligonaphthyl acrylate, oligopentachlorophenyl acrylate, and
oligophenyl acrylate. Examples of the oligomethacrylic acid esters
include oligomethyl methacrylate, oligoethyl methacrylate,
oligomethacrylonitrile, oligoadamantyl methacrylate, oligobenzyl
methacrylate, oligo-tert-butyl methacrylate, oligo-tert-butylphenyl
methacrylate, oligocycloethyl methacrylate, oligocyanoethyl
methacrylate, oligocyanomethylphenyl methacrylate, oligocyanophenyl
methacrylate, oligocyclobutyl methacrylate, oligocyclodecyl
methacrylate, oligocyclododecyl methacrylate, oligocyclobutyl
methacrylate, oligocyclohexyl methacrylate, oligocyclooctyl
methacrylate, oligofluoroalkyl methacrylate, oligoglycidyl
methacrylate, oligoisobornyl methacrylate, oligoisobutyl
methacrylate, oligophenyl methacrylate, oligotrimethylsilyl
methacrylate, and oligoxylenyl methacrylate. Examples of the
oligo-olefins include oligoethylene, oligopropylene, and
oligo-.alpha.-olefin. Examples of the oligosulfones include
oligophenyl sulfone, oligoether sulfone, and oligosulfone. Examples
of the oligoarylates include oligoarylate. Examples of the
oligoether ketones include oligoether ketone, oligoether ether
ketone, oligoether ketone ketone, and oligoether ether ketone
ketone. Examples of the oligoetherimides include oligoetherimide.
Examples of the oligophenylene sulfides include oligophenylene
sulfide. Examples of the oligophenylene ethers include
oligophenylene ether. Examples of the oligocarbonates include
oligocarbonate. Examples of the oligobenzimidazoles include
oligobenzimidazole. Examples of the oligofluoroethylenes include
oligotetrafluoroethylene, oligochlorotrifluoroethylene, and
oligovinylidene fluoride. The prefix "oligo-" means an oligomer
consisting of a few to dozen monomers. Multimers consisting of a
larger number of monomers than oligomers, that is, polymers, may
also be used as the first site.
[0023] The second site of the polymer includes a functional group
capable of forming a noncovalent bond. Examples of the noncovalent
bond include a hydrogen bond, a coordinate bond, and an ionic bond
(the same applies hereinafter). The second site may include a
plurality of functional groups capable of forming a noncovalent
bond or may be a polymer consisting of units including a functional
group capable of forming a noncovalent bond. The functional group
capable of forming a noncovalent bond is preferably a basic group
and is more preferably a nitrogen-containing heterocyclic group.
Examples of the nitrogen-containing heterocyclic group include a
pyridyl group, a benzimidazolyl group, a pyrimidyl group, an
imidazolyl group, a benzothiazolyl group, a benzoxazolyl group, an
oxadiazolyl group, a quinolyl group, a quinoxalyl group, and a
thiadiazolyl group. For example, in the case where the second site
includes a pyridyl group, polyvinylpyridines (functional group:
pyridyl group) and the like may be used. Examples of the
polyvinylpyridines include poly(2-vinylpyridine),
poly(3-vinylpyridine), and poly(4-vinylpyridine).
[0024] The polymer may be any type of polymer that includes at
least the first site and the second site; for example, the polymer
may be a block copolymer that includes the first site and the
second site or may be a random copolymer or multi-block copolymer
that includes the first site and the second site. Hereinafter, the
first site is referred to as "A-chain" and the second site is
referred to as "B-chain" for the sake of simplicity. In the case
where the polymer is an A-B diblock copolymer, the average degree
of polymerization of the A-chain is preferably 2 to 10000. If the
average degree of polymerization of the A-chain is less than the
lower limit, it becomes difficult to form a glassy or crystalline
domain. If the average degree of polymerization of the A-chain
exceeds the upper limit, it becomes difficult to handle the sample.
The average degree of polymerization of the A-chain is more
preferably 10 to 5000 and is particularly preferably 30 to 2000.
The average degree of polymerization of the B-chain is preferably 2
to 5000. If the average degree of polymerization of the B-chain is
less than the lower limit, it becomes difficult to uniformly form
the proton-conductive mixed phase by mixing the polymer with the
proton-conductive substance. If the average degree of
polymerization of the B-chain exceeds the upper limit, the acidity
of the proton-conductive mixed phase is reduced disadvantageously.
The average degree of polymerization of the B-chain is more
preferably 10 to 1000 and is particularly preferably 50 to 500. In
the case where the polymer is an A-B diblock copolymer, the
compositional ratio of the A-chain to the B-chain is preferably
99:1 to 10:90. If the compositional ratio does not fall within the
above range, the entirety of the proton-conductive membrane may
disadvantageously become grassy or, in another case, the
proton-conductive membrane may fail to form a soft elastomer and
become fluidized disadvantageously.
[0025] The proton-conductive substance includes a
proton-releasing/binding site (i.e., a third site) that is capable
of released protons and includes a functional group capable of
noncovalently binding to the second site of the polymer and a
proton coordination site (i.e., a fourth site) capable of
coordinating to the protons. The proton-releasing/binding site and
the proton coordination site are included in different molecules
that interact with each other (see FIG. 1) or being included in the
same molecule (see FIG. 2). The functional group of the
proton-releasing/binding site is preferably an acidic group in the
case where the functional group included in the second site of the
polymer is a basic group. Examples of the acidic group include a
carboxyl group, a phosphate group, a sulfo group, and a
sulfonylimide group. Among these, a sulfo group and a sulfonylimide
group are preferable. The amount of the proton-releasing/binding
site is excessively large compared with the amount of the second
site of the polymer. This increases the likelihood of free protons
generating from the proton-releasing/binding site and,
consequently, markedly contributes to the conduction of protons.
The proton coordination site preferably includes a functional group
that includes a lone pair and is capable of weakly coordinating to
protons. Examples of such a functional group include an ether
linkage, an ester group, an alcohol group, a ketone group, and an
amide group. Among these, an ether linkage and an alcohol group are
preferable.
[0026] The proton-conductive substance may be a mixture that
includes a substance X including the proton-releasing/binding site
and a nonaqueous substance Y including the proton coordination site
and interacting with the substance X (see FIG. 1). Since the
substance X is noncovalently bound to the second site of the
polymer and the substance Y interacts with the substance X, both
substances X and Y do not elute from the membrane. The substance X
is not limited. In the case where the functional group included in
the second site of the polymer is a basic group, the substance X
preferably includes an acidic group as a functional group. Examples
of the acidic group include a carboxyl group, a phosphate group, a
sulfo group, and a sulfonylimide group. Among these, a sulfo group
and a sulfonylimide group are preferable. The substance X is
particularly preferably selected from, for example, a polymer
having a side chain including a sulfo group and a fluorine compound
including a sulfonylimide group. The polymer having a side chain
including a sulfo group is preferably a perfluorocarbon polymer
having a side chain including a perfluoroalkyl portion including a
sulfo group (e.g., Nafion). The fluorine compound including a
sulfonylimide group is particularly preferably
bis(trifluoromethanesulfonyl)imide. The substance Y may be any
nonaqueous substance (i.e., any substance other than water) that
includes the proton coordination site and interacts with the
substance X. The substance Y is preferably selected from, for
example, a solvent including an ether linkage and a polymer
including an alcohol group. The solvent including an ether linkage
is preferably a protic solvent including an ether linkage. Examples
of such a protic solvent include hydroxy-terminated polyethylene
glycol, tetraethylene glycol, and triethylene glycol. Specifically,
the protic solvent may be a protic solvent in which hydrogen atoms
are replaced with fluorine atoms, such as Fomblin D2 (registered
trademark) produced by SOLVAY, that is, dihydroxy-terminated
perfluoropolyether, or Fluorolink C10 (registered trademark)
produced by SOLVAY, that is, carboxyl-terminated
perfluoropolyether. The polymer including an alcohol group is
preferably an acrylic acid polymer including an alcohol group. The
acrylic acid polymer may be a polymer consisting of one type of
monomer or a copolymer consisting of two or more types of monomers.
Examples of the monomer include (2-hydroxyethyl) acrylate and
(4-hydroxybutyl) acrylate. In the case where two or more types of
monomers are used, it is preferable that at least one of the
monomers be a monomer including two or more polymerizable
functional groups. When the monomer including two or more
polymerizable functional groups is used, a branched acrylic acid
copolymer including an alcohol group can be produced. This reduces
the flowability of the proton-conductive mixed phase and enhances a
shape retention property. Examples of the monomer including two or
more polymerizable functional groups include
N,N'-methylenebisacrylamide and divinylbenzene.
[0027] The proton-conductive substance may be a single pure
substance including the proton-releasing/binding site and the
proton coordination site in the same molecule (see FIG. 2). Since
the proton-releasing/binding site noncovalently binds to the second
site of the polymer, the above substance does not readily elute
from the membrane. The above proton-conductive substance is not
limited and is preferably, for example, a disulfonic acid including
an ether linkage. Examples of such a disulfonic acid include
3,3'-(propane-1,3-diylbis(oxy))bis(propane-1-sulfonic acid).
[0028] The proton-conductive substance and the polymer are selected
such that the glass-transition temperature of the proton-conductive
mixed phase, which includes the second site to which the
proton-releasing/binding site of the proton-conductive substance is
bound and the proton-conductive substance, is lower than the
service temperature of the non-humidified proton-conductive
membrane. This enables the proton-conductive mixed phase to melt
and conduct protons in a suitable manner during the use.
Furthermore, the membrane exhibits the properties of a soft
elastomer as a whole. The service temperature of the non-humidified
proton-conductive membrane may be set to be, for example,
50.degree. C., 100.degree. C., or a temperature higher than
150.degree. C., in the case where the glass-transition temperature
or melting temperature of the first site of the polymer is
sufficiently high.
[0029] A method for producing the non-humidified proton-conductive
membrane according to the embodiment is described below. In the
case where the proton-conductive substance is a mixture that
includes a substance X including the proton-releasing/binding site
and a nonaqueous substance Y including the proton coordination site
and interacting with the substance X, the non-humidified
proton-conductive membrane is produced in the following manner.
Specifically, the polymer is dissolved or dispersed in a solvent to
prepare a solution or dispersion of the polymer. This solvent is
preferably a solvent that relatively readily evaporates, such as an
alcohol solvent, an ether solvent, an ester solvent, a pyridine
solvent, water, or a mixed solvent including any combination of the
above solvents. The substance X and the substance Y are dissolved
or dispersed in a solvent to prepare a solution or dispersion of
the proton-conductive substance. This solvent is preferably a
solvent that relatively readily evaporates, such as an alcohol
solvent, an ether solvent, an ester solvent, a pyridine solvent,
water, or a mixed solvent including any combination of the above
solvents. The solution or dispersion of the polymer is mixed with
the solution or dispersion of the proton-conductive substance.
Subsequently, the solvents are evaporated. Hereby, a non-humidified
proton-conductive membrane is formed. In the case where the
substance Y is the acrylic acid polymer including an alcohol group,
it is preferable to mix the polymer that includes the first site
and the second site with the substance X and a monomer that is a
raw material for the acrylic acid polymer including an alcohol
group, which constitutes the substance Y, and polymerize the
resulting mixture in order to prevent the molten state of the
proton-conductive mixed phase from being degraded. In the case
where the acrylic acid polymer is a copolymer, it is preferable to
adequately adjust the amount of the monomer including two or more
polymerizable functional groups, which is capable of forming a
branched copolymer.
[0030] In the case where the proton-conductive substance is a
single pure substance that includes the proton-releasing/binding
site and the proton coordination site in the same molecule, the
non-humidified proton-conductive membrane is produced in the
following manner. Specifically, the polymer is dissolved or
dispersed in a solvent to prepare a solution or dispersion of the
polymer. This solvent is preferably a solvent that relatively
readily evaporates, such as an alcohol solvent, an ether solvent,
an ester solvent, a pyridine solvent, water, or a mixed solvent
including any combination of the above solvents. The single pure
substance that includes the proton-releasing/binding site and the
proton coordination site in the same molecule is dissolved or
dispersed in a solvent to prepare a solution or dispersion of the
proton-conductive substance. This solvent is preferably a solvent
that relatively readily evaporates, such as an alcohol solvent, an
ether solvent, an ester solvent, a pyridine solvent, water, or a
mixed solvent including any combination of the above solvents. The
solution or dispersion of the proton-conductive substance may
include an alcohol such as 1,3-propanediol, triethylene glycol,
tetraethylene glycol, or dihydroxy-terminated polyethylene glycol.
The solution or dispersion of the polymer is mixed with the
solution or dispersion of the proton-conductive substance.
Subsequently, the solvents are evaporated. Hereby, a non-humidified
proton-conductive membrane is formed.
[0031] A fuel cell that includes the non-humidified
proton-conductive membrane according to the embodiment is described
below with reference to FIG. 3. FIG. 3 is a cross-sectional view of
a fuel cell 10. The fuel cell 10 includes a membrane electrode
assembly (hereinafter, referred to as "MEA") 2 constituted by the
above-described non-humidified proton-conductive membrane 3 and
electrodes 4 and 5 disposed on the respective surfaces of the
proton-conductive membrane 3 and a pair of separators 6 and 7
between which the MEA 2 is interposed. The MEA 2 is constituted by
the non-humidified proton-conductive membrane 3 and the two
electrodes, that is, an anode 4 that serves as a fuel electrode and
a cathode 5 that serves as an oxygen electrode, between which the
proton-conductive membrane 3 is interposed. The anode 4 is
constituted by a catalyst layer 4a and a gas diffusion layer 4b.
The cathode 5 is constituted by a catalyst layer 5a and a gas
diffusion layer 5b. The catalyst layers 4a and 5a are located on
the sides of the respective electrodes on which the electrodes are
in contact with the non-humidified proton-conductive membrane 3 and
composed of conductive carbon black including platinum fine
particles. The gas diffusion layers 4b and 5b are disposed on the
catalyst layers 4a and 5a, respectively, and composed of carbon
cloth made of carbon fiber yarn. The platinum particles included in
the catalyst layers 4a and 5a facilitate the separation of hydrogen
into protons and electrons and a reaction in which oxygen combines
with protons and electrons to produce water; any substance other
than platinum which has the same function as platinum may be used.
The gas diffusion layers 4b and 5b may be composed of, instead of
carbon cloth, carbon paper or carbon felt made of carbon fibers and
are only required to have sufficiently high gas diffusibility and
sufficiently high electrical conductivity. The pair of separators 6
and 7 are composed of a gas-impermeable electrically conductive
member (e.g., carbon or a metal). The separator 6 has a fuel-gas
channel 6g which is formed in the surface that is in contact with
the anode 4 of the MEA 2 and through which a fuel gas is passed.
The separator 7 has an oxidation-gas channel 7g which is formed in
the surface that is in contact with the cathode 5 of the MEA 2 and
through which an oxidation gas is passed.
[0032] The power generation using the fuel cell 10 is described.
For generating electric power using the fuel cell 10, hydrogen that
serves as a fuel gas is fed from the outside of the fuel cell 10
into the fuel-gas channel 6g, while air that serves as an oxidation
gas is fed into the oxidation-gas channel 7g. Hydrogen passed
though the fuel-gas channel 6g is diffused in the gas diffusion
layer 4b of the anode 4 and reaches the catalyst layer 4a, in which
hydrogen is separated into protons and electrons. The protons
migrate to the cathode 5 through the non-humidified
proton-conductive membrane 3. The electrons migrate to the cathode
through an external circuit that is not illustrated in the
drawings. The air passed through the oxidation-gas channel 7g is
diffused in the gas diffusion layer 5b of the cathode 5 and reaches
the catalyst layer 5a. Subsequently, in the cathode 5, the protons
and electrons react with oxygen included in the air to produce
water. The above reaction produces an electromotive force. As
described above, it is not necessary to humidify the non-humidified
proton-conductive membrane 3 included in the fuel cell 10 with a
humidifier since the non-humidified proton-conductive membrane 3
exhibits proton conductivity even under a non-humidified
condition.
[0033] The present invention is not limited the examples described
above. It will be appreciated that the present invention can be
implemented in various forms so long as they fall within the
technical scope of the invention.
EXAMPLES
[0034] Examples of the present invention are described below. The
proton-conductive soft elastomer membranes prepared in Examples
correspond to the non-humidified proton-conductive membrane
according to the present invention. Table 1 summarizes the results
obtained in Examples and Comparative examples. Note that, Examples
below do not limit the present invention.
Example 1
[1] Preparation of Proton-Conducting Soft Elastomer Membrane
[0035] A polystyrene-b-poly(4-vinylpyridine) block copolymer
(hereinafter, referred to as "S4VP") synthesized by living anionic
polymerization was purchased from Polymer Source, Inc. The average
degree of polymerization of polystyrene was 2115. The average
degree of polymerization of poly(4-vinylpyridine) was 143. In 2.0 g
of a tetrahydrofuran (THF)/methanol (MeOH) mixed solvent with a
weight ratio of 7/3, 51 mg of S4VP was dissolved. Into a Teflon
beaker ("Teflon" is a registered trademark) having a volume of 10
mL, 2.30 g of a 10-wt % aqueous dispersion of Nafion (equivalent
mass: 1000) purchased from Aldrich was charged. The beaker was
placed on a hot plate heated at 70.degree. C. for 48 hours to
evaporate water. Subsequently, 240 mg of tetraethylene glycol (TEG)
was added to the beaker. To the beaker, 2.0 g of a THF/MeOH mixed
solvent with a weight ratio of 6/4 was further added in order to
dissolve Nafion in TEG/THF/MeOH. The S4VP/THF/MeOH solution was
mixed with the Nafion/TEG/THF/MeOH solution. No precipitate was
formed in the resulting liquid mixture. The liquid mixture was
placed on a hot plate heated at 60.degree. C. for 2 days in order
to evaporate THF/MeOH and perform casting. Hereby, a
proton-conductive soft elastomer membrane with a Nafion/TEG/S4VP
ratio of about 4.5/4.5/1 by weight was prepared. The amount of
sulfo groups included in Nafion was theoretically about 7.4 times
the amount of pyridyl groups included in S4VP.
[0036] FIG. 4 is a schematic diagram illustrating the
proton-conductive soft elastomer membrane. In FIG. 4, the
polystyrene portion corresponds to the first site of the polymer;
the poly(4-vinylpyridine) portion corresponds to the second site of
the polymer; Nafion corresponds to the substance x including the
proton-releasing/binding site; and TEG corresponds to the substance
Y including the proton coordination site. The Tg (glass-transition
temperature) of polystyrene was about 100.degree. C. The Tg of
poly(4-vinylpyridine) was about 150.degree. C. The Tg of Nafion was
about 130.degree. C. The melting point of TEG was about -6.degree.
C. The pyridyl groups included in poly(4-vinylpyridine) are
ionically bound to some of the sulfo groups included in Nafion.
Some of the sulfo groups included in Nafion are weakly bound to
oxygen atoms included in ether linkages of TEG by electrostatic
interaction. Some of the sulfo groups release protons to form
sulfonate ions. In Example 1, the proton-conductive mixed phase
(the portion surrounded by the one-dot chain line in FIG. 4) is a
mixture including Nafion, TEG, and poly(4-vinylpyridine) and fixed
to polystyrene. The proton-conductive mixed phase had a Tg equal to
or lower than room temperature and was therefore in a molten state
at the temperature (80.degree. C. or 95.degree. C., see [2] below)
at which alternating current impedance was measured. This
measurement temperature is considered as a service temperature of
the proton-conductive soft elastomer membrane.
[2] Measurement of Alternating Current Impedance
[0037] Platinum nets having a thickness of about 0.1 mm were used
as electrodes. The distance between the electrodes was set to 0.50
cm. The proton-conductive soft elastomer membrane was interposed
between the electrodes. The membrane had a thickness of 0.04 cm and
a width of 0.32 cm. The sample to be measured, which was interposed
between the electrodes, was placed in a natural convection
thermostatic drying oven. The sample was dried for about 6 hours
with the temperature of the drying oven being set to 60.degree. C.
Subsequently, the temperature (i.e., the measurement temperature)
of the drying oven was increased to 80.degree. C. After the
internal temperature of the drying oven had been stabilized, the
alternating current impedance of the sample was measured under a
non-humidified condition at a voltage of 80 mV while the frequency
was changed from 1000000 Hz to 1 Hz. The measurement was conducted
using a potentio/galvanostat VERSASTAT 4-400 with FRA (Prinston
Applied Research). The resistance of the sample determined from the
x-intercept of the Cole-Cole plot was 5.0.times.10.sup.4.OMEGA..
The proton conductivity of the sample calculated using the
relationship formula: Proton conductivity=Interelectrode
distance/(Membrane thickness.times.Membrane width.times.Resistance)
was 7.8.times.10.sup.-4 S/cm. After the temperature at which
alternating current impedance was measured had been increased to
95.degree. C., the sample had a resistance of 3.1.times.10.sup.4
S/cm and a proton conductivity of 1.3.times.10.sup.-3 S/cm. The
proton conductivity of the sample was increased when the
temperature was increased from 80.degree. C. to 95.degree. C. This
is presumably because, when the temperature was increased, the
viscosity of the proton-conductive mixed phase that was in a molten
state was reduced and, accordingly, the proton conductivity of the
sample was increased. During the measurement, the proton-conductive
soft elastomer membrane did not become fluidized and retained its
original shape as a whole.
TABLE-US-00001 TABLE 1 Measurement Proton Proton-conducting
temperature Resistance conductivity substance Polymer Mass ratio
[.degree. C.] [.OMEGA.] [S/cm] Example 1 Nafion + TEG S4VP
4.5/4.5/1.sup..asterisk-pseud.1 80 5.0 .times. 10.sup.4 7.8 .times.
10.sup.-4 95 3.1 .times. 10.sup.4 1.3 .times. 10.sup.-3 Comparative
Nafion + TEG -- 5.1/4.9/0.sup..asterisk-pseud.1
.sup..asterisk-pseud.3 Example 1 Comparative Nafion S4VP
6.7/0/3.3.sup..asterisk-pseud.1 80 .sup..asterisk-pseud.4 Example 2
Example 2 Nafion + TEG S4VP 4/4/2.sup..asterisk-pseud.1 80 1.2
.times. 10.sup.5 2.3 .times. 10.sup.-4 95 8.3 .times. 10.sup.4 3.3
.times. 10.sup.-4 Example 3 Nafion + TEG S4VP
6/3/1.sup..asterisk-pseud.1 80 8.3 .times. 10.sup.4 6.9 .times.
10.sup.-4 95 5.6 .times. 10.sup.4 1.0 .times. 10.sup.-3 Example 4
BSA(+PD) S2VP 4/4/2.sup..asterisk-pseud.2 80 4.1 .times. 10.sup.4
1.5 .times. 10.sup.-3 95 2.1 .times. 10.sup.4 2.8 .times. 10.sup.-3
65 6.1 .times. 10.sup.4 9.8 .times. 10.sup.-4 47 1.4 .times.
10.sup.5 4.3 .times. 10.sup.-4 Example 5 HTFSI + TEG + S2VP
4.06/2.94/2/1.sup..asterisk-pseud.5 80 7.0 .times. 10.sup.4 3.7
.times. 10.sup.-4 Alcohol group- 95 6.6 .times. 10.sup.4 3.9
.times. 10.sup.-4 containing acrylic acid copolymer
.sup..asterisk-pseud.1Mass ratio of Nafion/TEG/S4VP.
.sup..asterisk-pseud.2Mass ratio of BSA/PD/S2VP.
.sup..asterisk-pseud.3It could not be measured because it did
become fluidized. .sup..asterisk-pseud.4Resistance was extremely
large, and the proton conductivity was extremely low.
.sup..asterisk-pseud.5Mass ratio of HTFSI/TEG/Alcohol
group-containing acrylic acid copolymer/S2VP.
Comparative Example 1
[0038] Into a Teflon beaker having a volume of 10 mL, 2.52 g of a
10-wt % aqueous dispersion of Nafion (equivalent mass: 1000) was
charged. The beaker was placed on a hot plate heated at 70.degree.
C. for 48 hours to evaporate water. Subsequently, 240 mg of TEG was
added to the beaker. To the beaker, 2.0 g of a THF/MeOH mixed
solvent with a weight ratio of 6/4 was further added in order to
dissolve Nafion in TEG/THF/MeOH. The resulting solution was placed
on a hot plate heated at 60.degree. C. for 2 days in order to
evaporate THF/MeOH and perform casting. Hereby, a clayey mixture
consisting of Nafion and TEG which was uniform at room temperature
was prepared. When the clayey mixture was placed in a natural
convection thermostatic drying oven heated at 50.degree. C. in
order to measure the alternating current impedance of the clayey
mixture under a non-humidified condition, the clayey mixture became
fluidized. Therefore, it was not possible to determine the proton
conductivity of the clayey mixture in a solid state. It is
considered that, in Comparative example 1 where the
proton-conductive mixed phase was a mixture of Nafion with TEG,
fluidization occurred at 50.degree. C. because of absence of a
solid phase that supports the proton-conductive mixed phase.
Comparative Example 2
[0039] In 2.0 g of a THF/MeOH mixed solvent with a weight ratio of
7/3, 75 mg of S4VP purchased from Polymer Source, Inc. in which the
average degree of polymerization of polystyrene was 2115 and the
average degree of polymerization of poly(4-vinylpyridine) was 143
was dissolved. Into a Teflon beaker having a volume of 10 mL, 1.53
g of a 10-wt % aqueous dispersion of Nafion (equivalent mass: 1000)
was charged. The beaker was placed on a hot plate heated at
70.degree. C. for 48 hours to evaporate water. Subsequently, 2.0 g
of a THF/MeOH mixed solvent with a weight ratio of 6/4 was added to
the beaker in order to dissolve Nafion in THF/MeOH. The
S4VP/THF/MeOH solution was mixed with the Nafion/THF/MeOH solution.
No precipitate was formed in the resulting liquid mixture. The
liquid mixture was placed on a hot plate heated at 60.degree. C.
for 2 days in order to evaporate THF/MeOH and perform casting.
Hereby, a solid membrane was prepared. For measuring the
alternating current impedance of the membrane, a membrane having a
thickness of 0.04 cm and a width of 0.32 cm was prepared. The
membrane was interposed between electrodes such that the distance
between the electrodes was 0.50 cm and then placed in a natural
convection thermostatic drying oven. The temperature of the drying
oven was set to 80.degree. C. After the internal temperature of the
drying oven had been stabilized, the alternating current impedance
of the membrane was measured under a non-humidified condition at a
voltage of 80 mV while the frequency was changed from 1000000 Hz to
1 Hz. It was confirmed that the membrane had a considerably high
resistance and a considerably low proton conductivity. In
Comparative example 2, the component that corresponds to the
proton-conductive mixed phase is a mixture of Nafion with
poly(4-vinylpyridine). It is considered that the proton-conductive
mixed phase hardly conducted protons, since the Tg of the mixture
of Nafion with poly(4-vinylpyridine) was theoretically equal to or
higher than either of the Tg's of the two substances, that is,
130.degree. C. or more, and the proton-conductive mixed phase was
not in a molten state but in a solid state under a non-humidified
condition at 80.degree. C.
Example 2
[0040] In Example 2, a proton-conductive soft elastomer membrane
(weight ratio of Nafion/TEG/S4VP: about 4/4/2) was prepared as in
Example 1, except that, in [1] of Example 1, 101 mg of S4VP, 2.00 g
of a 10-wt % aqueous dispersion of Nafion (equivalent mass: 1000),
and 199 mg of TEG were used. The amount of sulfo groups included in
Nafion was theoretically about 3.3 times the amount of pyridyl
groups included in S4VP. The alternating current impedance of the
membrane was measured as in Example 1, except that, in [2] of
Example 1, the thickness of the membrane was changed to be 0.06 cm
and the width of the membrane was changed to be 0.33 cm. The
membrane had a resistance of 1.2.times.10.sup.5.OMEGA. and a proton
conductivity of 2.3.times.10.sup.-4 S/cm at 80.degree. C. The
membrane had a resistance of 8.3.times.10.sup.4.OMEGA. and a proton
conductivity of 3.3.times.10.sup.-4 S/cm at 95.degree. C. In
Example 2, the proton-conductive mixed phase was a mixture
including Nafion, TEG, and poly(4-vinylpyridine) and fixed to
polystyrene as in Example 1. The proton-conductive mixed phase had
a Tg equal to or lower than room temperature and was therefore in a
molten state at the temperature (80.degree. C. or 95.degree. C.) at
which alternating current impedance was measured. During the
measurement, the proton-conductive soft elastomer membrane prepared
in Example 2 did not become fluidized and retained its original
shape as a whole.
Example 3
[0041] In Example 3, a proton-conductive soft elastomer membrane
(weight ratio of Nafion/TEG/S4VP: about 6/3/1) was prepared as in
Example 1, except that, in [1] of Example 1, 50 mg of S4VP, 3.03 g
of a 10-wt % aqueous dispersion of Nafion (equivalent mass: 1000),
and 150 mg of TEG were used. The amount of sulfo groups included in
Nafion was theoretically about 9.8 times the amount of pyridyl
groups included in S4VP. The alternating current impedance of the
membrane was measured as in Example 1, except that, in [2] of
Example 1, the thickness of the membrane was changed to be 0.04 cm
and the width of the membrane was changed to be 0.21 cm. The
membrane had a resistance of 8.3.times.10.sup.4.OMEGA. and a proton
conductivity of 6.9.times.10.sup.-4 S/cm at 80.degree. C. The
membrane had a resistance of 5.6.times.10.sup.4.OMEGA. and a proton
conductivity of 1.0.times.10.sup.-3 S/cm at 95.degree. C. In
Example 3, the proton-conductive mixed phase was a mixture
including Nafion, TEG, and poly(4-vinylpyridine) and fixed to
polystyrene as in Example 1. The proton-conductive mixed phase had
a Tg equal to or lower than room temperature and was therefore in a
molten state at the temperature (80.degree. C. or 95.degree. C.) at
which alternating current impedance was measured. During the
measurement, the proton-conductive soft elastomer membrane prepared
in Example 3 did not become fluidized and retained its original
shape as a whole.
Example 4
[0042] In Example 4, a polystyrene-b-poly(2-vinylpyridine) block
copolymer (hereinafter, referred to as "S2VP") synthesized by
living anionic polymerization was used instead of S4VP used in [1]
of Example 1. The average degree of polymerization of polystyrene
was 1250. The average degree of polymerization of
poly(2-vinylpyridine) was 1285. Furthermore,
3,3'-(propane-1,3-diylbis(oxy))bis(propane-1-sulfonic acid)
(referred to as "BSA")/1,3-propanediol (referred to as "PD") was
used instead of Nafion/TEG. BSA was synthesized by a method
analogous to the schemes reported in Solid State Ionics, 1995, vol.
80, pp. 201-212 and Colloid Polymer Science, 2014, vol. 292, pp.
1261-1268. A proton-conductive soft elastomer membrane (weight
ratio of BSA/PD/S2VP: about 4/4/2) was prepared as in Example 1,
except that 97 mg of S2VP and 1.0 g of a THF/MeOH mixed solvent
with a weight ratio of 7/3 were used, 191 mg of BSA was used
instead of Nafion, 191 mg of PD was used instead of TEG, and 0.9 g
of a THF/MeOH mixed solvent with a weight ratio of 7/3 was used
instead of 2.0 g of a THF/MeOH mixed solvent with a weight ratio of
6/4. The amount of sulfo groups included in BSA was theoretically
about 2.5 times the amount of pyridyl groups included in S2VP. FIG.
5 is a schematic diagram illustrating the proton-conductive soft
elastomer membrane. In FIG. 5, the polystyrene portion corresponds
to the first site of the polymer; the poly(2-vinylpyridine) portion
corresponds to the second site of the polymer; and BSA corresponds
to the single proton-conductive substance including the
proton-releasing/binding site and the proton coordination site in
the same molecule. PD is omissible. The Tg (glass-transition
temperature) of polystyrene was about 100.degree. C. The Tg of
poly(2-vinylpyridine) was about 100.degree. C. The melting point of
BSA was room temperature or less. The melting point of PD was
-59.degree. C. The pyridyl groups included in poly(2-vinylpyridine)
are ionically bound to the sulfo groups included in BSA. In Example
4, the proton-conductive mixed phase, that is, a mixture including
BSA, PD, and poly(2-vinylpyridine), was fixed to polystyrene. It is
considered that PD electrostatically interacted with BSA. The
proton-conductive mixed phase that includes poly(2-vinylpyridine)
(the portion surrounded by the one-dot chain line in FIG. 5) had a
Tg equal to or lower than room temperature and was therefore in a
molten state at the temperature (47.degree. C. to 95.degree. C.) at
which alternating current impedance was measured.
[0043] The alternating current impedance of the soft elastomer
membrane was measured as in Example 1, except that, in [2] of
Example 1, the thickness of the membrane was changed to be 0.03 cm
and the width of the membrane was changed to be 0.28 cm. The
membrane had a resistance of 4.1.times.10.sup.4.OMEGA. and a proton
conductivity of 1.5.times.10.sup.-3 S/cm at 80.degree. C. The
membrane had a resistance of 2.1.times.10.sup.4.OMEGA. and a proton
conductivity of 2.8.times.10.sup.-3 S/cm at 95.degree. C. The
proton conductivity of the soft elastomer membrane was increased
when the temperature was increased from 80.degree. C. to 95.degree.
C. This is presumably because, when the temperature was increased,
the viscosity of the proton-conductive mixed phase that was in a
molten state was reduced and, accordingly, the proton conductivity
of the soft elastomer membrane was increased. The membrane had a
resistance of 6.1.times.10.sup.4.OMEGA. and a proton conductivity
of 9.8.times.10.sup.-4 S/cm at 65.degree. C. The membrane had a
resistance of 1.4.times.10.sup.5.OMEGA. and a proton conductivity
of 4.3.times.10.sup.-4 S/cm at 47.degree. C. The proton
conductivity of the soft elastomer membrane decreased with a
reduction in temperature. This is presumably because, when the
temperature was reduced, the viscosity of the proton-conductive
mixed phase that was in a molten state was increased and,
accordingly, the proton conductivity of the soft elastomer membrane
was reduced. During the measurement, the proton-conductive soft
elastomer membrane prepared in Example 4 did not become fluidized
and retained its original shape as a whole.
Example 5
[0044] Polystyrene-b-poly(2-vinylpyridine) (hereinafter, referred
to as "S2VP"), which corresponds to the A-B diblock copolymer, was
synthesized in accordance with the block copolymer synthesis method
(reversible addition-fragmentation chain transfer polymerization)
described in Macromolecules 45, 8013-8020 (2012). Measurement of
average degree of polymerization and molecular weight distribution
(Mw/Mn) was conducted by gel permeation chromatography (GPC) and
nuclear magnetic resonance spectroscopy. The average degree of
polymerization of polystyrene was 307. The average degree of
polymerization of poly(2-vinylpyridine) was 390. The molecule
weight distribution Mw/Mn of the copolymer was 1.39.
[0045] Subsequently, 50.3 mg of S2VP, 359 mg of a liquid mixture
(referred to as "HTFSI/TEG") including
bis(trifluoromethanesulfonyl)imide (referred to as "HTFSI") and
tetraethylene glycol (referred to as "TEG") which was prepared by
mixing HTFSI with TEG at a weight ratio of 58/42, 108 mg of
(2-hydroxyethyl) acrylate purified through a basic alumina column,
4.1 mg of N,N'-methylenebisacrylamide, 1.18 g of 1,4-dioxane used
as a solvent, and 0.1 mg of azobisisobutyronitrile (referred to as
"AIBN") used as a polymerization initiator were weighed and mixed
with one another in a sample bottle having a volume of 20 mL. The
weight ratio among S2VP, HTFSI/TEG, and the purified
(2-hydroxyethyl) acrylate was 1/7/2. The amount of sulfonylimide
groups included in HTFSI was theoretically about 2.7 times the
amount of pyridyl groups included in S2VP. The resulting mixture
was bubbled with nitrogen for 20 minutes and subsequently stirred
for 30 minutes at 500 rpm in an oil bath heated at 80.degree. C. to
copolymerize (2-hydroxyethyl) acrylate with
N,N'-methylenebisacrylamide. After a lapse of 30 minutes, the
rotation of the stir bar in the sample bottle stopped and the
sample bottle was subsequently immersed in the oil bath heated at
80.degree. C. for another 6 hours and 30 minutes in order to
maximize the reaction of unreacted monomers (i.e., (2-hydroxyethyl)
acrylate and N,N'-methylenebisacrylamide). Then, the sample bottle
was placed on a hot plate heated at 50.degree. C. for about 2 days
to perform solvent casting and subsequently vacuum-dried for
another 1 day to remove the solvent (i.e., 1,4-dioxane) and
unreacted monomers. Hereby, a proton-conductive soft elastomer
membrane was prepared.
[0046] Hereinafter, the copolymer of (2-hydroxyethyl) acrylate with
N,N'-methylenebisacrylamide is referred to as "alcohol
group-containing acrylic acid copolymer".
[0047] FIG. 6 is a schematic diagram illustrating the
proton-conductive soft elastomer membrane. In FIG. 6, the
polystyrene portion corresponds to the first site of the polymer;
the poly(2-vinylpyridine) portion corresponds to the second site of
the polymer; HTFSI corresponds to the substance X including the
proton-releasing/binding site; and TEG and the alcohol
group-containing acrylic acid copolymer correspond to the substance
Y including the proton coordination site. The Tg (glass-transition
temperature) of polystyrene was about 100.degree. C. The Tg of
poly(2-vinylpyridine) was about 100.degree. C. The Tg of a polymer
chain of the alcohol group-containing acrylic acid copolymer which
was derived from (2-hydroxyethyl) acrylate was about -15.degree. C.
The melting point of TEG was about -6.degree. C. The pyridyl groups
included in the poly(2-vinylpyridine) block of S2VP are ionically
bound to some of the sulfonylimide groups included in HTFSI. Some
of the sulfonylimide groups included in the HTFSI are weakly bound
to the oxygen atoms included in the ether linkages of TEG and
hydroxyl groups by electrostatic interaction. Some of the
sulfonylimide groups release protons to form imidide ions. In
Example 5, the proton-conductive mixed phase is a mixture including
HTFSI, TEG, the poly(2-vinylpyridine) block of S2VP, and the
alcohol group-containing acrylic acid copolymer and is fixed in
place by a hard domain constituted by the polystyrene block of
S2VP. The alcohol group-containing acrylic acid copolymer includes
branching points derived from N,N'-methylenebisacrylamide, which
reduce the flowability of the proton-conductive mixed phase and
enhance a shape retention property. The proton-conductive mixed
phase had a Tg equal to or lower than room temperature and was
therefore in a molten state at the temperature (80.degree. C. or
95.degree. C.) at which alternating current impedance was
measured.
[0048] The alternating current impedance of the soft elastomer
membrane was measured as in Example 1, except that, in [2] of
Example 1, the distance between the electrodes was changed to be
0.70 cm, the thickness of the membrane was changed to be 0.092 cm
and the width of the membrane was changed to be 0.30 cm. The
membrane had a resistance of 7.0.times.10.sup.4.OMEGA. and a proton
conductivity of 3.7.times.10.sup.-4 S/cm at 80.degree. C. After the
temperature at which alternating current impedance was measured had
been increased to 95.degree. C., the membrane had a resistance of
6.6.times.10.sup.4.OMEGA. and a proton conductivity of
3.9.times.10.sup.-4 S/cm. The proton conductivity of the membrane
was increased when the temperature was increased. This is
presumably because, when the temperature was increased, the
molecular mobility of the proton-conductive mixed phase that was in
a molten state was increased and, accordingly, the proton
conductivity of the membrane was increased. During the measurement,
no substance eluted from the proton-conductive membrane was
confirmed, and the proton-conductive membrane did not become
fluidized and retained its original shape.
[0049] The present application claims priority from Japanese Patent
Application No. 2016-085786 filed on Apr. 22, 2016, the entire
contents of which are incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0050] The present invention can be used in technical fields in
which proton-conductive membranes are used, such as the field of
fuel cells.
[0051] 10 fuel cell, 2 MEA, 3 non-humidified proton-conductive
membrane, 4 anode, 4a catalyst layer, 4b gas diffusion layer, 5
cathode, 5a catalyst layers, 5b gas diffusion layer, 6 separator,
6g fuel-gas channel, 7 separator, 7g oxidation-gas channel
* * * * *